1. Field of the Invention
The present invention relates to non-destructive probing and more particularly to a non-destructive probing system for probing non-destructively and accurately for search objects buried in a matrix containing dielectric material, non-destructive probing method, program for conducting non-destructive probes, and computer-readable storage medium for storing the program.
2. Background Art
Radar probing which involves sending electromagnetic waves, especially high-frequency electromagnetic waves, into a matrix containing dielectric material and non-destructively inspecting or probing for search objects or cavities buried in the matrix finds applications in various fields because of its capability to probe for search objects non-destructively.
Normally, radar probing generates radar reflection signals by placing a transmit/receive antenna used as a probe adjacent to the surface of the matrix in which search objects are buried and detecting reflections from the search objects buried in the matrix.
However, radar reflection signals are affected by various noises including external noise and internally generated equipment noise. Consequently, when analyzing radar reflection signals to check for the presence of any search object, it is difficult to distinguish between noise and the search object. Various attempts have been made so far to solve this problem. For example, Published Unexamined Japanese Patent Application No. 2000-258549 discusses a method for improving probing accuracy by calculating differential signals through comparison of radar reflection signals with background signals. FIG. 1 summarizes a process of removing background signals.
According to the conventional process shown in FIG. 1, radar reflection signals are acquired in Step 101. Then in Step 102, background signals are calculated by averaging radar reflection signals including the reflected signals from search objects. In Step 103, the differential signals between the average background signal and all the radar reflection signals are calculated and in Step 104, radar reflection signals free of background influence is obtained.
Also, Published Unexamined Japanese Patent Application No. 2001-4668 discloses a waveform observation apparatus and method for calculating average waveform data from a plurality of measured waveforms and displaying measured waveform data and average waveform data.
The methods described above can undoubtedly improve the accuracy of probing for search objects by removing background effectively. In radar probing, however, the surface of a matrix may be extremely uneven, i.e., bumpy, or a matrix may be composed of soil mixed with substances such as sand, gravel, or ballast exposed to the surface. In that case, it is not possible to bring a probe in contact with the ground surface completely. Consequently, direct coupling signals and signals reflected from the matrix surface are picked up in addition to the signals reflected from the search object.
Even in such cases, the influence of the variations in the signals reflected from the matrix surface can be reduced if the matrix surface can be flattened. However, it is not always possible to flatten the matrix surface to be probed by radar.
For example, at the time of removing small antipersonnel mines, it is necessary to probe, with high sensitivity and high accuracy, for the locations of small antipersonnel mines buried in various fields while preserving the matrix surface such as soil. In such cases, the reflection from the matrix surface such as soil is also observed as radar reflection signals together with the signals reflected from the buried search objects, i.e., the small antipersonnel mines. It is nevertheless necessary to minimize the influence of the signals reflected from the matrix surface and detect the search objects buried in the matrix with very high sensitivity and high accuracy.
Besides, although it is possible to take measurement by increasing the distance between the matrix surface and probe so much as to eliminate the influence caused by irregularities on the matrix surface, this will reduce measurement accuracy. Also, it is not always easy to keep the distance constant.
Under these circumstances, there has been demand for a system, a method, a program for executing the method, and a computer-readable storage medium storing the program which make it possible to detect or probe for search objects by radiating electromagnetic waves into a matrix and receiving radar reflection while ensuring sufficiently high sensitivity and accuracy even if the practical distance between the matrix surface and probe varies and non-destructively preserving the condition of the matrix surface.
Specifically, a feature of the present invention provides a non-destructive probing system for non-destructively probing for a search object buried in a matrix containing dielectric material by radiating electromagnetic waves to the above described matrix, including: a probe which is disposed in opposing relation to a surface of the above described matrix, radiates electromagnetic waves to the above described matrix, and detects radar reflection signals formed by reflection of the above described electromagnetic waves, and signal processing means for calculating the signal reflected by the search object from the above described radar reflection signals, wherein the above described signal processing means comprises: a unit for forming designated groups from the above described radar reflection signals, a storage unit for storing the above described designated groups of radar reflection signals individually, a unit for calculating a standard background signal from each of the above described designated groups of radar reflection signals stored individually, a unit for calculating a differential signal between each of the above described radar reflection signals and the above described standard background signal separately for each of the above described designated groups, and a unit for identifying the signal reflected from the above described search object out of the above described differential signal.
Another feature of the present invention provides a method for non-destructively probing for a search object buried in a matrix containing dielectric material by disposing a probe with respect to the above described matrix and radiating electromagnetic waves from the above described probe to the above described matrix, comprising the steps of: disposing an antenna in opposing relation to a surface of the above described matrix; radiating electromagnetic waves from the above described probe to the above described matrix and detecting radar reflection signals; forming designated groups from the above described radar reflection signals; storing the above described radar reflection signals by dividing them into the above described designated groups; determining a standard background signal for each of the above described designated groups; calculating a differential signal between each of the above described radar reflection signals belonging to the above described selected group and the above described standard background signal; and extracting the signal reflected by the above described buried search object from the above described differential signal.
Still another feature of the present invention provides a program for executing a non-destructive probing method comprising a step of disposing a probe in opposing relation to a surface of a matrix which contains dielectric material, a step of radiating electromagnetic waves from the above described probe to the matrix and detecting radar reflection signals, and a step of processing radar reflection signals which contain reflection from a search object by using signal processing means, wherein the above described program makes the above described signal processing means execute the steps of: radiating electromagnetic waves from the above described probe to the matrix and detecting radar reflection signals; forming designated groups from the above described radar reflection signals; storing the above described radar reflection signals by dividing them into the above described designated groups; determining a standard background signal for each of the above described designated groups; calculating a differential signal between each of the above described radar reflection signals belonging to the above described selected group and the above described standard background signal; and extracting the signal reflected by the above described buried search object from the above described differential signal.
Yet still another feature of the present invention provides a computer-readable storage medium that records a program for executing a non-destructive probing method comprising a step of disposing a probe in opposing relation to a surface of a matrix which contains dielectric material, a step of radiating electromagnetic waves from the above described probe to the matrix and detecting radar reflection signals, and a step of processing radar reflection signals which contain reflection from a search object by using signal processing means, wherein the above described storage medium makes the above described signal processing means execute the steps of: radiating electromagnetic waves from the above described antenna to the matrix and detecting radar reflection signals; forming designated groups from the above described radar reflection signals; storing the above described radar reflection signals by dividing them into the above described designated groups; determining a standard background signal for each of the above described designated groups; calculating a differential signal between each of the above described radar reflection signals belonging to the above described selected group and the above described standard background signal; and extracting the signal reflected by the above described buried search object from the above described differential signal.
Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views.